This invention relates to a method of magnetic recording using a magnetic recording medium, such as a magnetic tape, including a step of testing characteristics of the magnetic medium by recording a test signal, and Featured by a step of determining whether such a test signal can be recorded without erasing a previously recorded signal. The invention also relates to a magnetic recording and reproducing device, such as a video tape recorder, e.g., a video cassette recorder, that is used for implementing such a method.
Video tape cassettes of various grades used for video recording by a video cassette recorder are available. To ensure successful recording on all grades of tape, conventional video cassette recorders have often been designed to match the frequency characteristics of the lowest-grade tape. This is to prevent inverted white peaks with whatever type of tape is used and ensure a sufficient signal-to-noise ratio. Such video cassette recorders, however, fail to take full advantage of the superior characteristics of higher-grade tape.
This will be explained with reference to FIG. 15 and FIG. 16. FIG. 15 shows the frequency characteristics of two tapes, a high-grade tape A and a lower-grade tape B. The horizontal axis indicates frequency. The vertical axis indicates power received from the magnetic heads, before demodulation. Both tapes show a diminishing response at higher frequencies, but tape A provides a higher playback level at all frequencies, and particularly at high Frequencies. If the record circuit is adjusted to match the characteristics of the tape B, the frequency characteristics of the video signal reproduced from the tape A and tape B are as shown in FIG. 16.
Despite the fact that the tape A has superior frequency characteristics, the signal reproduced from the tape A shows characteristics inferior to those of the signal reproduced from the tape B if the signals are recorded under condition matched the tape B. It does not necessarily mean that tape B gives a better reproduced picture than tape A, because tape A has a higher signal-to-noise ratio. It is however obvious that the superior frequency characteristics of tape A shown in FIG. 15 are not being properly utilized.
One scheme that addresses this problem equips a video cassette recorder to record and reproduce a test signal, thereby sense tape characteristics, and adjust its own recording characteristics to take optimum advantage of the characteristics of the tape. For instance, prior to recording, a test signal is recorded and reproduced to assess or determine the frequency characteristics of the tape, and an equalizer or the like in the recording circuit is controlled in accordance with the result of the assessment.
The present invention is directed to certain problems that arise when this scheme is implemented. One problem is that signals that are already recorded on the tape may be undesirably erased when the test signal is recorded. Another problem is that circuits used for implementing the test is complex and expensive.